1. Field of the Invention
The present invention relates to a new remote control cable or wire, which is light, of small section, with high tensile strength, virtually inextensible, flexible and impervious, which can advantageously be used for the transmission of control commands for moving bodies traveling at high speed.
More particularly, it relates to a new remote control cable intended to guide a moving body by means of commands which are in the form of rectangular electrical signals, a specific length of the cable being stored at the rear of the moving body and unwinding as the body moves.
The invention also relates to a new process and a new device for making such a cable.
2. Technical Considerations and Prior Art
Numerous documents describe conducting wires or conducting cables which can be used to transmit commands to a moving body. Amongst these documents are French Pat. No. 1,477,500 and its two Patents of Addition Nos. 90,970 and 93,154.
French Pat. No. 1,477,500 describes an inextensible conducting cable comprising a core containing at least two separate conductors situated virtually along the longitudinal axis of the said cable, the core being surrounded by a layer of lapping and the assembly covered by at least one thin coating layer.
According to Addition No. 90,970, in order to hold the conductors apart, the conducts are arranged symmetrically relative to a bonded glass fibre core and bonded to the latter by heat sealing. Other reinforcing glass fibres are arranged parallel to the core/conductor assembly and, as in the principal patent, the whole structure is surrounded by a lapping wire and an external coating. Preferably, the conducting wires are slightly inlaid inside the central core.
Addition No. 93,154 relates to improvements to the conducting cables produced according to the processes mentioned above, these improvements applying principally to, on the one hand, the nature and the method of lapping and, on the other hand, to the external coating of the said cable.
The conducting cables described in the aforementioned documents exhibit very high qualities, particularly with respect to their fineness, their strength and, above all, with respect to their electrical properties and particularly to their time constant factor.
However, the symmetrical positioning of the conducting wires relative to the core is rather difficult to achieve and, during manufacture and/or use, the wires can move slightly, which is prejudicial to good transmission of signals. Moreover, the use of glass fibres, as a separating element and as the core, increases the weight of the cable substantially, which leads to a reduction in the breaking coefficient of the cable determined by the ratio of the breaking strength of the cable to the weight of the cable.
To overcome these disadvantages, it has been proposed, particularly in French Pat. No. 2,005,693, to hold and to separate the conducting wires of a cable of the type previously described by assembling them in parallel by bonding them with the same lacquer as that used to insulate each of the wires. If, in theory, such a solution is attractive, it must be recognized that, from the practical point of view, it is difficult to achieve and that it suffers from a certain number of disadvantages. Indeed with this method, it is virtually impossible to have a good bond between the two conductors along their whole length, since the bonding takes place over a very small part of the surface of each of the conductors. Moreover, this bonding is rather poor and the conductors may have a tendency to separate from one another in use. Finally, the spacing between the two conductors is provided by the thickness of the insulating layer which surrounds each conductor, which therefore requires the conductors to be covered with a relatively thick layer of insulating material if sufficient spacing between them is to be achieved.
The prior art further includes the following patents: German Pat. No. 1,540,626, filed Dec. 23, 1965 (Ser. No. 101,140); German Pat. No. 1,665,605, filed Apr. 14, 1966 (Ser. No. 103,167); French Pat. No. 1,564,336 (based on U.S. Pat. Application Ser. No. 640,621), filed May 23, 1967; and U.S. Pat. No. 3,536,548, filed Aug. 26, 1968 (Ser. No. 755,296).